This invention relates to the art of coating compositions and to a method for providing surfaces with coatings. This invention is particularly applicable to ultra thin films formed by amphiphilic molecules and will be described with specific reference thereto. However, it will be appreciated that certain features of the invention have broader aspects, and may be used with other types of film forming substances and coating compositions.
The forming of ultra thin, self-assembling molecular films from compositions containing amphiphilic molecules, and methods for modifying substrate surfaces with these films, are described in our commonly assigned U.S. Pat. Nos. 5,078,791; 5,106,561; 5,166,000; 5,300,561; 5,173,365; 5,204,126; and 5,219,654, the disclosures of which are hereby incorporated by reference. These ultra thin films are advantageous for coating non-porous surfaces of glass, plastics, ceramics, porcelain, fiberglass and metals, to provide scratch resistance, corrosion protection, anti-reflective optics, friction reduction, print priming, moisture barriers, and the like. For example, the films may be used for coating laboratory glassware and for providing a non-stick coating for pots, pans, dishes or utensils. The films are particularly advantageous for use on plastic eyewear lenses, such as those manufactured of aliphatic and polycarbonate resins that are pre-treated with a hard coat for scratch resistance.
As particularly disclosed in U.S. Pat. No. 5,078,791 and 5,219,654, substrate surfaces can be treated with a composition comprising amphiphilic molecules dispersed in a non-aqueous carrier, such as petrolatum, mineral jelly, hydrogenated animal or vegetable oil, or the like. The carrier has a gel state at a temperature of about 20.degree. C. that is sufficient to inhibit diffusion of moisture and/or oxygen into the composition and to maintain a uniform dispersion of the amphiphilic molecules throughout the carrier. The composition, in the gel state, is typically applied to the substrate surface at room temperature by wiping, brushing, rolling, spraying, or the use of a doctor blade. Upon application to the substrate surface, the amphiphilic molecules automatically separate from the composition by chemically attractive forces between the molecules and the substrate surface, and spontaneously self-assemble in-situ and chemically bond to the substrate surface to form a substantially continuous thin film of substantially uniform thickness not greater than about 0.5 microns. After a treatment time period, typically 15 minutes to one hour, the excess coating composition is washed away. The film forming substances may be self-polymerizing in-situ or may contain polymerizable moieties that are cross-linkable by heating, photochemical reaction and/or the use of a catalyst.
The above approach has been shown to be effective for applying an ultra thin film coating to substrates having non-porous, i.e. glass or glass-like, surfaces that are chemically reactive with the film forming substance. In the context of this invention, a chemically reactive surface is a surface that has a sufficient number of chemical moieties available to bond with the amphiphilic molecules, such that the amphiphilic molecules self-assemble on the surface, chemically bond to the chemical moieties, and are in close enough proximity to self-polymerize. to form a substantially continuous thin surface film. For example, plastic eyewear lenses made of CR-39 (PPG Industries) have chemically reactive surfaces that can be successfully coated with the ultra thin films. Lenses that are pre-treated with a chemical "hard coat" (e.g. polysiloxanes or acrylics) for scratch resistance also can be coated with the continuous thin film if the hard coat is chemically reactive with the film forming substance. However, the application of these ultra thin films is currently limited to chemically reactive surfaces.
Surfaces that have inadequate chemical reactivity (i.e. surfaces having an insufficient number of available chemically reactive groups for bonding with the amphiphilic molecules, such that the bound molecules are not in close enough proximity to self-polymerize and form a continuous film) are not coatable by the processes described above. In addition, surfaces that ordinarily would be chemically reactive but that are pre-treated with hard coats that are chemically unreactive or have inadequate chemical reactivity, are also not presently coatable. In the context of the invention, chemically unreactive surfaces are those with substantially no available chemical moieties capable of chemically bonding amphiphilic molecules.
Moreover, current methods employing a gel composition may not readily allow efficient surface coating of relatively inaccessible areas in odd-shaped articles. The current processes are also time-consuming due to the slow mobility of the amphiphilic molecules in the gel consistency of the carrier. The processes are also not sufficiently economical for use in large scale commercial treatment applications.